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The role of albedo and accumulation in the 2010melting record in GreenlandTo cite this article M Tedesco et al 2011 Environ Res Lett 6 014005

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IOP PUBLISHING ENVIRONMENTAL RESEARCH LETTERS

Environ Res Lett 6 (2011) 014005 (6pp) doi1010881748-932661014005

The role of albedo and accumulation in the2010 melting record in Greenland

M Tedesco1 X Fettweis23 M R van den Broeke3R S W van de Wal3 C J P P Smeets3 W J van de Berg3M C Serreze4 and J E Box56

1 The City College of New York CUNY New York NY USA2 University of Liege Liege Belgium3 Institute for Marine and Atmospheric Research Utrecht (IMAU) Utrecht University UtrechtThe Netherlands4 National Snow and Ice Data Center Boulder CO USA5 Department of Geography Ohio State University Columbus OH USA6 Byrd Polar Research Center Ohio State University Columbus OH USA

Received 1 December 2010Accepted for publication 7 January 2011Published 21 January 2011Online at stacksioporgERL6014005

AbstractAnalyses of remote sensing data surface observations and output from a regional atmospheremodel point to new records in 2010 for surface melt and albedo runoff the number of dayswhen bare ice is exposed and surface mass balance of the Greenland ice sheet especially overits west and southwest regions Early melt onset in spring triggered by above-normalnear-surface air temperatures contributed to accelerated snowpack metamorphism andpremature bare ice exposure rapidly reducing the surface albedo Warm conditions persistedthrough summer with the positive albedo feedback mechanism being a major contributor tolarge negative surface mass balance anomalies Summer snowfall was below average Thishelped to maintain low albedo through the 2010 melting season which also lasted longer thanusual

Keywords Greenland melting surface mass balance albedo accumulation

1 Introduction and objectives

Large positive near-surface temperature anomalies occurredalong the coast of the Greenland ice sheet during the year 2010(eg Box et al 2010) For example at Aasiaat (6842prime35primeprimeN5252prime10primeprimeW) along Greenlandrsquos west coast 2010 as a wholewas the warmest since records began in 1951 with records alsoset for winter spring May and June Narsarssuaq (6109prime39primeprimeN4525prime32primeprimeW) in southern Greenland saw its warmest winterand spring its warmest May and its warmest annual averagesince records began in 1951 Nuuk the capital of Greenlandlocated along the southwest coast (6410prime30primeprimeN 5144prime20primeprimeW)with a temperature time series extending back to 1873 sawrecord warmth for winter spring summer and the year as awhole (Cappelen 2010)

Surface melting over the Greenland ice sheet which canbe estimated from satellite data ground observations or models

(Abdalati and Steffen 1997 Mote 2007 Nghiem et al 2001Hall et al 2009 Tedesco 2007 Hanna et al 2008 Fettweiset al 2010b Ettema et al 2010) was also exceptional in2010 (Box et al 2010) Results obtained by applying thealgorithm reported in Tedesco (2007) to spaceborne microwavebrightness temperatures (eg Armstrong et al 1994 Knowleset al 2002) are consistent with those reported in Box et al(2010) showing that large areas of the ablation zone in southGreenland underwent melting up to 50 days longer in 2010compared to the 1979ndash2009 average with melting in 2010starting exceptionally early at the end of April and ending quitelate in mid September (figure 1) These results are confirmedby surface measurements

Near-surface air temperature is often used as a proxy forsurface melting Previous studies have analyzed exceptionalmelting events mainly focusing on the relationship betweenmelt and near-surface temperatures (eg Mote 2007 Tedesco

1748-932611014005+06$3300 copy 2011 IOP Publishing Ltd Printed in the UK1

Environ Res Lett 6 (2011) 014005 M Tedesco et al

Figure 1 (a) anomaly map of melting days for 2010 derived from passive microwave data Hatched regions indicate where MAR-simulatedmeltwater production exceeds the mean by at least two standard deviations (b) time series of the daily melt extent for the 2010 season the1979ndash2009 average and the year 2007 (c) standardized melting index (the number of melting days times area subject to melting) for 2010from passive microwave data over the whole ice sheet and for different elevation bands

2007) However melting and the surface mass balance(SMB) also depend on accumulation radiation conditionsrefreezing and sublimation the latter relatively small andconstant in time (Box and Steffen 2001 Fettweis 2007 vanden Broeke et al 2008) Surface melt and albedo are intimatelylinked as melting increases so does snow grain size leadingto a decrease in surface albedo which then fosters furthermelt Also changes in accumulation can affect the seasonalevolution of surface albedo which influences the SMB Itis hence not sufficient to analyze near-surface temperaturetrends to understand the driving mechanisms of extrememass loss and studying the role of albedo and accumulationbecomes crucial to provide a more robust understandingof the exceptional melting detected by satellite microwavesensors

In this study we report results derived from spacebornesensors surface glaciological observations and regionalatmospheric model outputs regarding the surface albedoaccumulation and bare ice exposure over the Greenland icesheet during the summer of 2010 Our results indicate thatnegative surface albedo anomalies were especially prominentover west Greenland with bare ice exposed earlier thanprevious years In addition increased runoff and reducedaccumulation likely contributed to a strongly negative SMB

2 Data and methodologies

21 Satellite data

We use the moderate-resolution imaging spectroradiometer(MODIS) 16-day gridded albedo product (httpwww-modisbuedubrdfuserguideintrohtml) to study anomalies in bothdirectional hemispherical reflectance (black-sky albedo)and bi-hemispherical reflectance (white-sky albedo) in theshortwave visible and near-infrared bands Black-sky albedois the albedo under direct illumination (or direct beamcontribution) whereas white-sky albedo is the one underdiffuse or indirect light Black- and white-sky albedos canbe combined as a function of the diffuse skylight for arepresentation of the actual albedo such as measured by fieldinstruments (Lucht et al 2000) The MODIS product whichhas been evaluated over Greenland (eg Stroeve et al 2005)is provided every 8 days using 16 days acquisitions from boththe TERRA and AQUA satellites Data are provided on a 005latitudelongitude grid While we discuss only the shortwavewhite-sky albedo the conclusions that follow also apply toblack-sky visible and near-infrared albedos

22 Glaciological data

The Institute of Marine and Atmospheric Research Utrecht(IMAU) installed several automatic weather stations (AWSs)

2

Environ Res Lett 6 (2011) 014005 M Tedesco et al

Figure 2 (a) MODIS shortwave white-sky albedo anomalies for 2010 relative to 2004ndash2009 means for MayndashAugust (b) MAR estimatedstandardized anomalies (relative to 1979ndash2009) of the number of days with bare ice exposed for the period MayndashSeptember(c) MayndashSeptember snowfall anomalies from MAR relative to 1979ndash2009 means

along the Kangerlussuaq transect (K-transect 67N) insouthwest Greenland in August 2003 located at increasingdistance from the ice sheet margin and increasing elevationsup to 1500 m asl (van den Broeke et al 2008) This part ofGreenland is characterized by a 100 km wide ablation zone andan average equilibrium line altitude (ELA) of approximately1500 m asl The stations are equipped with radiation sensorsSMB can be estimated at the local spatial scale from stakesand acoustic height rangers Apart from atmospheric radiationthe stations measure basic meteorological variables like windspeed and direction temperature relative humidity and airpressure SMB measurements are performed along the K-transect at selected sites The three AWS sites (S5 S6 andS9) are located respectively 6 km (S5) 37 km (S6) and 91 km(S9) from the ice sheet margin at an elevation of 490 m (S5)1020 m (S6) and 1520 m (S9) asl Mass balance sites (S4SHR S7 S8 S10) are located 3 km (S4) 14 km (SHR) 52 km(S7) 63 km (S8) and 143 km (S10) from the ice sheet marginat an elevation of 340390 m (S4 340 m was the initial value)710 m (SHR) 1110 m (S7) 1260 m (S8) and 1850 m (S10)asl Mass balance data are available over the period 1991ndash2010 Weather station data are available for the period 2003ndash2010 Further information on the stations can be found in vande Wal et al (2005)

23 The surface and energy balance model

The surface and energy balance model is the regional climatemodel MAR (Modele Atmospherique Regional) coupledto the 1D Surface Vegetation Atmosphere Transfer scheme

SISVAT (Soil Ice Snow Vegetation Atmosphere Transfer) Theschemes and the set-up employed for the present study arefully described in Fettweis et al (2010a) Fettweis (2007) andLefebre et al (2005) Differently from most existing modelsMAR is coupled to a snow physical model called CROCUS(Brun et al 1992) CROCUS is a one-dimensional multi-layered energy balance model consisting of a thermodynamicmodule a water balance module taking into account therefreezing of meltwater a snow metamorphism module asnowice discretization module and an integrated surfacealbedo module For this study MAR outputs are derivedat a spatial resolution of 25 km for the period 1958ndash2010The ERA-40 reanalysis (1957ndash2001) the ERA-INTERIMreanalysis (2002ndashJune 2010) and after that the operationalanalysis (July 2010ndashSeptember 2010) from ECMWF are usedto initialize the meteorological fields at the beginning of thesimulation in September 1957 and to force every 6 h thelateral boundaries with temperature specific humidity andwind components during the simulation The sea surfacetemperatures (SST) and the sea-ice extent in the SISVATmodule are also prescribed by the reanalyses No re-initialization or correction are applied to the model outputsThe (re)analysis data are available every 6 h at a resolution ofat least 1 The MAR spatial domain is represented by an areaof 2000 km times 3500 km centered at 70N latitude and 40Wlongitude There are at least ten pixels between the Greenlandand the model boundaries The integration domain is shownin Fettweis et al (2005) An ice sheet mask is then applied toanalyze only those pixels belonging to the ice sheet (Fettweis2008) Outputs from the MAR model have been shown to

3

Environ Res Lett 6 (2011) 014005 M Tedesco et al

be consistent with results obtained from passive microwaveobservations (Fettweis et al 2010b)

3 Results and discussion

Figure 2(a) shows the MODIS shortwave white-sky albedoanomaly for the months of MayndashAugust (MJJA) relative tothe 2004ndash2009 mean This period was chosen because groundalbedo measurements for comparison are available startingin 2004 The MODIS record itself spans a longer period2001ndash2009 The strong negative albedo anomalies along thesouthwest margin of the ice sheet (more than minus010) areconsistent with the positive melting anomalies detected by themicrowave sensors and simulated by the MAR model (seefigure 1) As assessed using the complete MODIS record theshortwave 2010 albedo averaged over MJJA was up to 015below the mean over southwest Greenland with the largestnegative anomalies during August August albedo anomaliesare as large as minus025 near the Nuuk area and minus02 alongmost of the southwestern regions of the Greenland Ice SheetThe observed 2010 albedo anomalies can be the consequenceof (1) a reduced frequency andor amount of snowfall(2) enhanced melting and (3) exposure of bare ice for alonger period of time during the melting season Figure 2(b)provides the standardized anomaly map (the departure fromthe mean divided by the standard deviation of the distribution)of the number of days when bare ice was exposed in 2010based on MAR outputs According to MAR in 2010 bareice was exposed for a period up to four times longer than thestandard deviation computed over the 1979ndash2009 period alongthe western region of the ice sheet with absolute anomaliespeaking up to 50 days Figure 2(c) shows the summersnowfall anomalies (in mm water equivalent WE) from MARstill relative to 1979ndash2009 means The model suggests thatsummer accumulation in 2010 over the southwestern part ofthe Greenland ice sheet was two standard deviations belowthe 1979ndash2009 mean This together with large positive near-surface temperature anomalies very likely led to the prematureexposure of bare ice (figure 2(b)) and the reduced albedo(figure 2(a))

Figure 3(a) summarizes MAR estimates and measure-ments on the ice of SMB (mWE) averaged over four IMAUAWSs (SHR S6 S8 and S9) Data from the AWSs indicatethat average SMB values in 2010 were 23 standard deviationsbelow the 1991ndash2010 average (the record from the stationsbegin in 1991) Moreover according to MAR average SMBvalues in 2010 at the IMAU stations locations were 23standard deviations below the average over the same periodFor both measured and modeled quantities the SMB in 2010was the lowest for the data record As an example figure 3(b)shows the time series of MODIS and IMAU surface albedosfor 2010 together with the 2004ndash2009 average values at the S9station (6703prime02primeprimeN 4813prime53primeprimeW 1500 m asl) Differencesin absolute values from the satellite and ground observationsreflect the spatial scale at which MODIS data are collected orre-gridded atmospheric corrections and the MODIS albedoretrieval algorithm The figure highlights that both MODISand the station data show a decline in albedo through the 2010

Figure 3 (a) SMB from MAR and from sonic height ranger data(K-transect) for 1991ndash2009 averaged over the S9 S8 S6 and SHRstations (b) time series of MODIS shortwave albedo (black lineswith circles) and albedo at the IMAU sites (gray lines with squares)for 2010 at the S9 station Dotted lines indicate averages for2004ndash2009 (c) data from the sonic height ranger collected every halfan hour over the last 7 years (September 2003ndashSeptember 2010) atthe S9 station

melting season with the absence of sporadic peaks that wouldresult from snowfall events (which are present during yearswhen positive anomalies of summer snowfall are measured andmodeled) The match between the seasonal trends derived fromMODIS and those measured on the ice lends credence to theMAR results pointing to negative snowfall anomalies for 2010(figure 2(c)) and premature exposure of bare ice (figure 2(b))

Early exposure of bare ice and reduced snowfall in 2010are also evident from surface height measurements along theK-transect Figure 3(c) illustrates surface height changes overthe years 2003ndash2010 at the S9 station We focus on the stationS9 as it is situated at 1500 m elevation at the approximate

4

Environ Res Lett 6 (2011) 014005 M Tedesco et al

Figure 4 Monthly standardized anomalies for 2010 (relative to 1979ndash2009) for near-surface temperature albedo snowfall meltwater bareice area and melt area excluding bare ice simulated by MAR

ELA where annual accumulation should on average equalablation From figure 3(c) the net annual surface heightchange for the years 2004 2007 and 2008 is close to 0 m(indicating that the position of the ELA was close to thestation elevation) contrasting with the years of 2005 and2006 when the net surface height change was sim03ndash04 m(indicating that the station was above the ELA for those years)Reduced accumulation and exceptionally large ablation during2010 are evident The surface height data clearly indicatethat accumulation for 2010 at the S9 station was only about06 m (versus the 2003ndash2009 average of sim105 m) and thesurface height value recorded at the end of August was minus07 m(versus the 2003ndash2009 average of simminus005 m) below any valuepreviously recorded The total change in surface height wassim13 m the highest loss over the past twenty years Theextreme nature of the SMB loss in 2010 is also evident at theother stations along the K-transect (not shown here)

The MAR allows us to examine conditions back to 1958placing 2010 in the context of a longer time series Accordingto MAR the hydrological year (OctoberndashSeptember) 2009ndash2010 SMB anomaly set a new record low of minus310 Gt 26standard deviations below the 1958ndash2009 average surpassingthe previous record of 23 standard deviations set in 2007Snowfall for the period 1 October 2009ndash30 September 2010was about 68 Gt (15 standard deviations below average) andrunoff was 243 Gt or 24 standard deviations above the 1958ndash2009 average Figure 4 shows monthly standardized anomaliesfor 2010 (using 1979ndash2009 as a reference for consistencywith the passive microwave data time series) from MAR ofnear-surface temperature albedo snowfall meltwater bare icearea and melt area excluding bare ice Snowfall and near-surface temperature anomalies for the autumn and winter of2009 (SeptemberndashApril) are also reported as a reference Themodel indicates that surface albedo was persistently belowthe average (two standard deviations) for the summer Themeltwater produced in May (August) was sim3 (sim25) standard

deviations above the mean Bare ice area in May wassim35 standard deviations above the mean and it remainedpersistently around two standard deviations above averagethrough summer By contrast the melt area excluding bareice was exceptional in May August and September

4 Conclusions

Our analysis of remote sensing data surface glaciologicalobservations and model outputs paints a portrait of stronglynegative surface mass balance during 2010 promoted by astrong warmth and enhanced by large negative anomalies ofalbedo and accumulation and large positive anomalies of dayswhen bare ice was exposed Our results clearly indicatethat beside near-surface temperature other factors must beconsidered to properly analyze extreme events such as theone that occurred in 2010 The melt season started in midApril after a warm and dry winter Early melt onset triggeredby large positive near-surface temperature anomalies duringMay 2010 (up to +4 C above the mean) contributed toaccelerated snowpack metamorphism and premature bare iceexposure with the consequence of rapidly reducing the surfacealbedo Reduced accumulation in 2010 and the positive albedofeedback mechanism are likely responsible for the prematureexposure of bare ice While June and July temperatureanomalies were not exceptional being +15 C above the1979ndash2009 average anomalously warm conditions persistedwith the positive albedo feedback mechanism contributing tolarge negative SMB anomalies Summer snowfall which helpsto increase surface albedo was below average Melt duringAugust and September was also exceptional consistent withlow surface albedos and near-surface temperature anomalies ofup to +3 C yielding a long ablation season

The surface melt time series from the combined passivemicrowave record 1979ndashpresent is characterized by anupward trend with considerable year-to-year variability

5

Environ Res Lett 6 (2011) 014005 M Tedesco et al

primarily related to atmospheric conditions Viewed in thiscontext the unusually warm conditions over the Greenlandice sheet in 2010 and reduced snowfall can be related topersistence of a 500 hPa high ridge from late spring throughsummer Averaged for MayndashAugust 500 hPa heights wereabove normal over all of Greenland with the largest anomaliesof up to 80 m over the south-central ice sheet This anomalousridge was associated with 700 hPa temperature anomaliesover south-central Greenland of up to +3 C The ridge andassociated 700 hPa temperature anomaly was best expressed inMay and August coinciding with near-surface air temperaturerecords

Acknowledgments

This work was supported by NSF grants ANS 0909388 andARC 0901962 the NASA Cryosphere Program and the OhioState University Climate Water and Carbon Program Fieldwork along the K-transect has been supported by NWOALW

References

Abdalati W and Steffen K 1997 Snowmelt on the greenland ice sheetas derived from passive microwave satellite data J Climate10 165ndash75

Armstrong R L Knowles K W Brodzik M J and Hardman M A 1994DMSP SSMI Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media) updated 2009

Box J E Cappelen J Decker D Fettweis X Mote T Tedesco M andvan de Wal R S W 2010 Greenland (in Arctic Report Card 2010available at wwwarcticnoaagovreportcard)

Box J E and Steffen K 2001 Sublimation estimates for the Greenlandice sheet using automated weather station observationsJ Geophys Res 106 33965ndash82

Brun E David P Sudul M and Brunot G 1992 A numerical model tosimulate snowcover stratigraphy for operational Avalancheforecasting J Glaciol 38 13ndash22

Cappelen J 2010 DMI monthly climate data collection 1768ndash2009Denmark The Faroe Islands and Greenland Dansk MeterologiskInstitut Technical Report No 10-05 (available at wwwdmidkdmitr10-05pdf)

Ettema J van den Broeke M R van Meijgaard E van de Berg W JBox J E and Steffen K 2010 Climate of the Greenland ice sheetusing a high-resolution climate modelmdashpart 1 evaluationCryosph Discuss 4 561ndash602

Fettweis X 2007 Reconstruction of the 1979ndash2006 Greenland icesheet surface mass balance using the regional climate modelMAR The Cryosphere 1 21ndash40

Fettweis X 2008 Impact of ice sheet mask and resolution onestimating the surface mass balance of the Greenland ice sheetProc European Geophysical Union General Assembly (ViennaApril 2008) (available at httporbiulgacbebitstream2268367521Fettweis-2008-EGU-Poster2pdf)

Fettweis X Gallee H Lefebre L and van Ypersele J P 2005Greenland surface mass balance simulated by a regional climatemodel and comparison with satellite derived data in 1990ndash1991Clim Dyn 24 623ndash40

Fettweis X Mabille G Erpicum M Nicolay S andvan den Broeke M 2010a The 1958ndash2009 Greenland ice sheetsurface melt and the mid-tropospheric atmospheric circulationClim Dyn 36 139ndash59

Fettweis X Tedesco M van den Broeke M and Ettema J 2010bMelting trends over the Greenland ice sheet (1958ndash2009) fromspaceborne microwave data and regional climate modelsCryosph Discuss 4 2433ndash73

Hall D K Nghiem S V Schaaf C B DiGirolamo N E andNeumann G 2009 Evaluation of surface and near-surface meltcharacteristics on the Greenland ice sheet using MODIS andQuikSCAT data J Geophys Res 114 F04006

Hanna E Huybrechts P Steffen K Cappelen J Huff R Shuman CIrvine-Fynn T Wise S and Griffiths M 2008 Increased runofffrom melt from the Greenland ice sheet a response to globalwarming J Climate 21 331ndash41

Knowles K W Ein G Njoku E Armstrong R L and Brodzik M J2002 Nimbus-7 SMMR Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media)

Lefebre F Fettweis X Gallee H van Ypersele J Marbaix PGreuell W and Calanca P 2005 Evaluation of a high-resolutionregional climate simulation over Greenland Clim Dyn25 99ndash116

Lucht W Schaaf C B and Strahler A H 2000 An algorithm for theretrieval of albedo from space using semiempirical BRDFmodels IEEE Trans Geosci Remote Sens 38 977ndash98

Mote T L 2007 Greenland surface melt trends 1973ndash2007 evidenceof a large increase in 2007 Geophys Res Lett 34 L22507

Nghiem S V Steffen K Kwok R and Tsai W Y 2001 Detection ofsnowmelt regions on the Greenland ice sheet using diurnalbackscatter change J Glaciol 47 539ndash47

Stroeve J C Box J Gao F Liang S Nolin A and Schaaf C 2005Accuracy assessment of the MODIS 16-albedo product forsnow comparison with Greenland in situ measurements RemoteSens Environ 94 46ndash60

Tedesco M 2007 Snowmelt detection over the Greenland ice sheetfrom SSMI brightness temperature daily variations GeophysRes Lett 34 L02504

van de Wal R S W Greuell W van den Broeke M Reijmer C H andOerlemans J 2005 Surface mass-balance observations andautomatic weather station data along a transect nearKangerlussuaq West Greenland Ann Glaciol 42 311ndash6

van den Broeke M R Smeet C J P P Ettema J van der Veen Cvan de Wal R S W and Oerlemans J 2008 Partitioning of energyand meltwater fluxes in the ablation zone of the west Greenlandice sheet The Cryosphere 2 179ndash89

6

Environ Res Lett 6 (2011) 014005 M Tedesco et al

be consistent with results obtained from passive microwaveobservations (Fettweis et al 2010b)

3 Results and discussion

Figure 2(a) shows the MODIS shortwave white-sky albedoanomaly for the months of MayndashAugust (MJJA) relative tothe 2004ndash2009 mean This period was chosen because groundalbedo measurements for comparison are available startingin 2004 The MODIS record itself spans a longer period2001ndash2009 The strong negative albedo anomalies along thesouthwest margin of the ice sheet (more than minus010) areconsistent with the positive melting anomalies detected by themicrowave sensors and simulated by the MAR model (seefigure 1) As assessed using the complete MODIS record theshortwave 2010 albedo averaged over MJJA was up to 015below the mean over southwest Greenland with the largestnegative anomalies during August August albedo anomaliesare as large as minus025 near the Nuuk area and minus02 alongmost of the southwestern regions of the Greenland Ice SheetThe observed 2010 albedo anomalies can be the consequenceof (1) a reduced frequency andor amount of snowfall(2) enhanced melting and (3) exposure of bare ice for alonger period of time during the melting season Figure 2(b)provides the standardized anomaly map (the departure fromthe mean divided by the standard deviation of the distribution)of the number of days when bare ice was exposed in 2010based on MAR outputs According to MAR in 2010 bareice was exposed for a period up to four times longer than thestandard deviation computed over the 1979ndash2009 period alongthe western region of the ice sheet with absolute anomaliespeaking up to 50 days Figure 2(c) shows the summersnowfall anomalies (in mm water equivalent WE) from MARstill relative to 1979ndash2009 means The model suggests thatsummer accumulation in 2010 over the southwestern part ofthe Greenland ice sheet was two standard deviations belowthe 1979ndash2009 mean This together with large positive near-surface temperature anomalies very likely led to the prematureexposure of bare ice (figure 2(b)) and the reduced albedo(figure 2(a))

Figure 3(a) summarizes MAR estimates and measure-ments on the ice of SMB (mWE) averaged over four IMAUAWSs (SHR S6 S8 and S9) Data from the AWSs indicatethat average SMB values in 2010 were 23 standard deviationsbelow the 1991ndash2010 average (the record from the stationsbegin in 1991) Moreover according to MAR average SMBvalues in 2010 at the IMAU stations locations were 23standard deviations below the average over the same periodFor both measured and modeled quantities the SMB in 2010was the lowest for the data record As an example figure 3(b)shows the time series of MODIS and IMAU surface albedosfor 2010 together with the 2004ndash2009 average values at the S9station (6703prime02primeprimeN 4813prime53primeprimeW 1500 m asl) Differencesin absolute values from the satellite and ground observationsreflect the spatial scale at which MODIS data are collected orre-gridded atmospheric corrections and the MODIS albedoretrieval algorithm The figure highlights that both MODISand the station data show a decline in albedo through the 2010

Figure 3 (a) SMB from MAR and from sonic height ranger data(K-transect) for 1991ndash2009 averaged over the S9 S8 S6 and SHRstations (b) time series of MODIS shortwave albedo (black lineswith circles) and albedo at the IMAU sites (gray lines with squares)for 2010 at the S9 station Dotted lines indicate averages for2004ndash2009 (c) data from the sonic height ranger collected every halfan hour over the last 7 years (September 2003ndashSeptember 2010) atthe S9 station

melting season with the absence of sporadic peaks that wouldresult from snowfall events (which are present during yearswhen positive anomalies of summer snowfall are measured andmodeled) The match between the seasonal trends derived fromMODIS and those measured on the ice lends credence to theMAR results pointing to negative snowfall anomalies for 2010(figure 2(c)) and premature exposure of bare ice (figure 2(b))

Early exposure of bare ice and reduced snowfall in 2010are also evident from surface height measurements along theK-transect Figure 3(c) illustrates surface height changes overthe years 2003ndash2010 at the S9 station We focus on the stationS9 as it is situated at 1500 m elevation at the approximate

4

Environ Res Lett 6 (2011) 014005 M Tedesco et al

Figure 4 Monthly standardized anomalies for 2010 (relative to 1979ndash2009) for near-surface temperature albedo snowfall meltwater bareice area and melt area excluding bare ice simulated by MAR

ELA where annual accumulation should on average equalablation From figure 3(c) the net annual surface heightchange for the years 2004 2007 and 2008 is close to 0 m(indicating that the position of the ELA was close to thestation elevation) contrasting with the years of 2005 and2006 when the net surface height change was sim03ndash04 m(indicating that the station was above the ELA for those years)Reduced accumulation and exceptionally large ablation during2010 are evident The surface height data clearly indicatethat accumulation for 2010 at the S9 station was only about06 m (versus the 2003ndash2009 average of sim105 m) and thesurface height value recorded at the end of August was minus07 m(versus the 2003ndash2009 average of simminus005 m) below any valuepreviously recorded The total change in surface height wassim13 m the highest loss over the past twenty years Theextreme nature of the SMB loss in 2010 is also evident at theother stations along the K-transect (not shown here)

The MAR allows us to examine conditions back to 1958placing 2010 in the context of a longer time series Accordingto MAR the hydrological year (OctoberndashSeptember) 2009ndash2010 SMB anomaly set a new record low of minus310 Gt 26standard deviations below the 1958ndash2009 average surpassingthe previous record of 23 standard deviations set in 2007Snowfall for the period 1 October 2009ndash30 September 2010was about 68 Gt (15 standard deviations below average) andrunoff was 243 Gt or 24 standard deviations above the 1958ndash2009 average Figure 4 shows monthly standardized anomaliesfor 2010 (using 1979ndash2009 as a reference for consistencywith the passive microwave data time series) from MAR ofnear-surface temperature albedo snowfall meltwater bare icearea and melt area excluding bare ice Snowfall and near-surface temperature anomalies for the autumn and winter of2009 (SeptemberndashApril) are also reported as a reference Themodel indicates that surface albedo was persistently belowthe average (two standard deviations) for the summer Themeltwater produced in May (August) was sim3 (sim25) standard

deviations above the mean Bare ice area in May wassim35 standard deviations above the mean and it remainedpersistently around two standard deviations above averagethrough summer By contrast the melt area excluding bareice was exceptional in May August and September

4 Conclusions

Our analysis of remote sensing data surface glaciologicalobservations and model outputs paints a portrait of stronglynegative surface mass balance during 2010 promoted by astrong warmth and enhanced by large negative anomalies ofalbedo and accumulation and large positive anomalies of dayswhen bare ice was exposed Our results clearly indicatethat beside near-surface temperature other factors must beconsidered to properly analyze extreme events such as theone that occurred in 2010 The melt season started in midApril after a warm and dry winter Early melt onset triggeredby large positive near-surface temperature anomalies duringMay 2010 (up to +4 C above the mean) contributed toaccelerated snowpack metamorphism and premature bare iceexposure with the consequence of rapidly reducing the surfacealbedo Reduced accumulation in 2010 and the positive albedofeedback mechanism are likely responsible for the prematureexposure of bare ice While June and July temperatureanomalies were not exceptional being +15 C above the1979ndash2009 average anomalously warm conditions persistedwith the positive albedo feedback mechanism contributing tolarge negative SMB anomalies Summer snowfall which helpsto increase surface albedo was below average Melt duringAugust and September was also exceptional consistent withlow surface albedos and near-surface temperature anomalies ofup to +3 C yielding a long ablation season

The surface melt time series from the combined passivemicrowave record 1979ndashpresent is characterized by anupward trend with considerable year-to-year variability

5

Environ Res Lett 6 (2011) 014005 M Tedesco et al

primarily related to atmospheric conditions Viewed in thiscontext the unusually warm conditions over the Greenlandice sheet in 2010 and reduced snowfall can be related topersistence of a 500 hPa high ridge from late spring throughsummer Averaged for MayndashAugust 500 hPa heights wereabove normal over all of Greenland with the largest anomaliesof up to 80 m over the south-central ice sheet This anomalousridge was associated with 700 hPa temperature anomaliesover south-central Greenland of up to +3 C The ridge andassociated 700 hPa temperature anomaly was best expressed inMay and August coinciding with near-surface air temperaturerecords

Acknowledgments

This work was supported by NSF grants ANS 0909388 andARC 0901962 the NASA Cryosphere Program and the OhioState University Climate Water and Carbon Program Fieldwork along the K-transect has been supported by NWOALW

References

Abdalati W and Steffen K 1997 Snowmelt on the greenland ice sheetas derived from passive microwave satellite data J Climate10 165ndash75

Armstrong R L Knowles K W Brodzik M J and Hardman M A 1994DMSP SSMI Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media) updated 2009

Box J E Cappelen J Decker D Fettweis X Mote T Tedesco M andvan de Wal R S W 2010 Greenland (in Arctic Report Card 2010available at wwwarcticnoaagovreportcard)

Box J E and Steffen K 2001 Sublimation estimates for the Greenlandice sheet using automated weather station observationsJ Geophys Res 106 33965ndash82

Brun E David P Sudul M and Brunot G 1992 A numerical model tosimulate snowcover stratigraphy for operational Avalancheforecasting J Glaciol 38 13ndash22

Cappelen J 2010 DMI monthly climate data collection 1768ndash2009Denmark The Faroe Islands and Greenland Dansk MeterologiskInstitut Technical Report No 10-05 (available at wwwdmidkdmitr10-05pdf)

Ettema J van den Broeke M R van Meijgaard E van de Berg W JBox J E and Steffen K 2010 Climate of the Greenland ice sheetusing a high-resolution climate modelmdashpart 1 evaluationCryosph Discuss 4 561ndash602

Fettweis X 2007 Reconstruction of the 1979ndash2006 Greenland icesheet surface mass balance using the regional climate modelMAR The Cryosphere 1 21ndash40

Fettweis X 2008 Impact of ice sheet mask and resolution onestimating the surface mass balance of the Greenland ice sheetProc European Geophysical Union General Assembly (ViennaApril 2008) (available at httporbiulgacbebitstream2268367521Fettweis-2008-EGU-Poster2pdf)

Fettweis X Gallee H Lefebre L and van Ypersele J P 2005Greenland surface mass balance simulated by a regional climatemodel and comparison with satellite derived data in 1990ndash1991Clim Dyn 24 623ndash40

Fettweis X Mabille G Erpicum M Nicolay S andvan den Broeke M 2010a The 1958ndash2009 Greenland ice sheetsurface melt and the mid-tropospheric atmospheric circulationClim Dyn 36 139ndash59

Fettweis X Tedesco M van den Broeke M and Ettema J 2010bMelting trends over the Greenland ice sheet (1958ndash2009) fromspaceborne microwave data and regional climate modelsCryosph Discuss 4 2433ndash73

Hall D K Nghiem S V Schaaf C B DiGirolamo N E andNeumann G 2009 Evaluation of surface and near-surface meltcharacteristics on the Greenland ice sheet using MODIS andQuikSCAT data J Geophys Res 114 F04006

Hanna E Huybrechts P Steffen K Cappelen J Huff R Shuman CIrvine-Fynn T Wise S and Griffiths M 2008 Increased runofffrom melt from the Greenland ice sheet a response to globalwarming J Climate 21 331ndash41

Knowles K W Ein G Njoku E Armstrong R L and Brodzik M J2002 Nimbus-7 SMMR Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media)

Lefebre F Fettweis X Gallee H van Ypersele J Marbaix PGreuell W and Calanca P 2005 Evaluation of a high-resolutionregional climate simulation over Greenland Clim Dyn25 99ndash116

Lucht W Schaaf C B and Strahler A H 2000 An algorithm for theretrieval of albedo from space using semiempirical BRDFmodels IEEE Trans Geosci Remote Sens 38 977ndash98

Mote T L 2007 Greenland surface melt trends 1973ndash2007 evidenceof a large increase in 2007 Geophys Res Lett 34 L22507

Nghiem S V Steffen K Kwok R and Tsai W Y 2001 Detection ofsnowmelt regions on the Greenland ice sheet using diurnalbackscatter change J Glaciol 47 539ndash47

Stroeve J C Box J Gao F Liang S Nolin A and Schaaf C 2005Accuracy assessment of the MODIS 16-albedo product forsnow comparison with Greenland in situ measurements RemoteSens Environ 94 46ndash60

Tedesco M 2007 Snowmelt detection over the Greenland ice sheetfrom SSMI brightness temperature daily variations GeophysRes Lett 34 L02504

van de Wal R S W Greuell W van den Broeke M Reijmer C H andOerlemans J 2005 Surface mass-balance observations andautomatic weather station data along a transect nearKangerlussuaq West Greenland Ann Glaciol 42 311ndash6

van den Broeke M R Smeet C J P P Ettema J van der Veen Cvan de Wal R S W and Oerlemans J 2008 Partitioning of energyand meltwater fluxes in the ablation zone of the west Greenlandice sheet The Cryosphere 2 179ndash89

6

Environ Res Lett 6 (2011) 014005 M Tedesco et al

Figure 4 Monthly standardized anomalies for 2010 (relative to 1979ndash2009) for near-surface temperature albedo snowfall meltwater bareice area and melt area excluding bare ice simulated by MAR

ELA where annual accumulation should on average equalablation From figure 3(c) the net annual surface heightchange for the years 2004 2007 and 2008 is close to 0 m(indicating that the position of the ELA was close to thestation elevation) contrasting with the years of 2005 and2006 when the net surface height change was sim03ndash04 m(indicating that the station was above the ELA for those years)Reduced accumulation and exceptionally large ablation during2010 are evident The surface height data clearly indicatethat accumulation for 2010 at the S9 station was only about06 m (versus the 2003ndash2009 average of sim105 m) and thesurface height value recorded at the end of August was minus07 m(versus the 2003ndash2009 average of simminus005 m) below any valuepreviously recorded The total change in surface height wassim13 m the highest loss over the past twenty years Theextreme nature of the SMB loss in 2010 is also evident at theother stations along the K-transect (not shown here)

The MAR allows us to examine conditions back to 1958placing 2010 in the context of a longer time series Accordingto MAR the hydrological year (OctoberndashSeptember) 2009ndash2010 SMB anomaly set a new record low of minus310 Gt 26standard deviations below the 1958ndash2009 average surpassingthe previous record of 23 standard deviations set in 2007Snowfall for the period 1 October 2009ndash30 September 2010was about 68 Gt (15 standard deviations below average) andrunoff was 243 Gt or 24 standard deviations above the 1958ndash2009 average Figure 4 shows monthly standardized anomaliesfor 2010 (using 1979ndash2009 as a reference for consistencywith the passive microwave data time series) from MAR ofnear-surface temperature albedo snowfall meltwater bare icearea and melt area excluding bare ice Snowfall and near-surface temperature anomalies for the autumn and winter of2009 (SeptemberndashApril) are also reported as a reference Themodel indicates that surface albedo was persistently belowthe average (two standard deviations) for the summer Themeltwater produced in May (August) was sim3 (sim25) standard

deviations above the mean Bare ice area in May wassim35 standard deviations above the mean and it remainedpersistently around two standard deviations above averagethrough summer By contrast the melt area excluding bareice was exceptional in May August and September

4 Conclusions

Our analysis of remote sensing data surface glaciologicalobservations and model outputs paints a portrait of stronglynegative surface mass balance during 2010 promoted by astrong warmth and enhanced by large negative anomalies ofalbedo and accumulation and large positive anomalies of dayswhen bare ice was exposed Our results clearly indicatethat beside near-surface temperature other factors must beconsidered to properly analyze extreme events such as theone that occurred in 2010 The melt season started in midApril after a warm and dry winter Early melt onset triggeredby large positive near-surface temperature anomalies duringMay 2010 (up to +4 C above the mean) contributed toaccelerated snowpack metamorphism and premature bare iceexposure with the consequence of rapidly reducing the surfacealbedo Reduced accumulation in 2010 and the positive albedofeedback mechanism are likely responsible for the prematureexposure of bare ice While June and July temperatureanomalies were not exceptional being +15 C above the1979ndash2009 average anomalously warm conditions persistedwith the positive albedo feedback mechanism contributing tolarge negative SMB anomalies Summer snowfall which helpsto increase surface albedo was below average Melt duringAugust and September was also exceptional consistent withlow surface albedos and near-surface temperature anomalies ofup to +3 C yielding a long ablation season

The surface melt time series from the combined passivemicrowave record 1979ndashpresent is characterized by anupward trend with considerable year-to-year variability

5

Environ Res Lett 6 (2011) 014005 M Tedesco et al

primarily related to atmospheric conditions Viewed in thiscontext the unusually warm conditions over the Greenlandice sheet in 2010 and reduced snowfall can be related topersistence of a 500 hPa high ridge from late spring throughsummer Averaged for MayndashAugust 500 hPa heights wereabove normal over all of Greenland with the largest anomaliesof up to 80 m over the south-central ice sheet This anomalousridge was associated with 700 hPa temperature anomaliesover south-central Greenland of up to +3 C The ridge andassociated 700 hPa temperature anomaly was best expressed inMay and August coinciding with near-surface air temperaturerecords

Acknowledgments

This work was supported by NSF grants ANS 0909388 andARC 0901962 the NASA Cryosphere Program and the OhioState University Climate Water and Carbon Program Fieldwork along the K-transect has been supported by NWOALW

References

Abdalati W and Steffen K 1997 Snowmelt on the greenland ice sheetas derived from passive microwave satellite data J Climate10 165ndash75

Armstrong R L Knowles K W Brodzik M J and Hardman M A 1994DMSP SSMI Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media) updated 2009

Box J E Cappelen J Decker D Fettweis X Mote T Tedesco M andvan de Wal R S W 2010 Greenland (in Arctic Report Card 2010available at wwwarcticnoaagovreportcard)

Box J E and Steffen K 2001 Sublimation estimates for the Greenlandice sheet using automated weather station observationsJ Geophys Res 106 33965ndash82

Brun E David P Sudul M and Brunot G 1992 A numerical model tosimulate snowcover stratigraphy for operational Avalancheforecasting J Glaciol 38 13ndash22

Cappelen J 2010 DMI monthly climate data collection 1768ndash2009Denmark The Faroe Islands and Greenland Dansk MeterologiskInstitut Technical Report No 10-05 (available at wwwdmidkdmitr10-05pdf)

Ettema J van den Broeke M R van Meijgaard E van de Berg W JBox J E and Steffen K 2010 Climate of the Greenland ice sheetusing a high-resolution climate modelmdashpart 1 evaluationCryosph Discuss 4 561ndash602

Fettweis X 2007 Reconstruction of the 1979ndash2006 Greenland icesheet surface mass balance using the regional climate modelMAR The Cryosphere 1 21ndash40

Fettweis X 2008 Impact of ice sheet mask and resolution onestimating the surface mass balance of the Greenland ice sheetProc European Geophysical Union General Assembly (ViennaApril 2008) (available at httporbiulgacbebitstream2268367521Fettweis-2008-EGU-Poster2pdf)

Fettweis X Gallee H Lefebre L and van Ypersele J P 2005Greenland surface mass balance simulated by a regional climatemodel and comparison with satellite derived data in 1990ndash1991Clim Dyn 24 623ndash40

Fettweis X Mabille G Erpicum M Nicolay S andvan den Broeke M 2010a The 1958ndash2009 Greenland ice sheetsurface melt and the mid-tropospheric atmospheric circulationClim Dyn 36 139ndash59

Fettweis X Tedesco M van den Broeke M and Ettema J 2010bMelting trends over the Greenland ice sheet (1958ndash2009) fromspaceborne microwave data and regional climate modelsCryosph Discuss 4 2433ndash73

Hall D K Nghiem S V Schaaf C B DiGirolamo N E andNeumann G 2009 Evaluation of surface and near-surface meltcharacteristics on the Greenland ice sheet using MODIS andQuikSCAT data J Geophys Res 114 F04006

Hanna E Huybrechts P Steffen K Cappelen J Huff R Shuman CIrvine-Fynn T Wise S and Griffiths M 2008 Increased runofffrom melt from the Greenland ice sheet a response to globalwarming J Climate 21 331ndash41

Knowles K W Ein G Njoku E Armstrong R L and Brodzik M J2002 Nimbus-7 SMMR Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media)

Lefebre F Fettweis X Gallee H van Ypersele J Marbaix PGreuell W and Calanca P 2005 Evaluation of a high-resolutionregional climate simulation over Greenland Clim Dyn25 99ndash116

Lucht W Schaaf C B and Strahler A H 2000 An algorithm for theretrieval of albedo from space using semiempirical BRDFmodels IEEE Trans Geosci Remote Sens 38 977ndash98

Mote T L 2007 Greenland surface melt trends 1973ndash2007 evidenceof a large increase in 2007 Geophys Res Lett 34 L22507

Nghiem S V Steffen K Kwok R and Tsai W Y 2001 Detection ofsnowmelt regions on the Greenland ice sheet using diurnalbackscatter change J Glaciol 47 539ndash47

Stroeve J C Box J Gao F Liang S Nolin A and Schaaf C 2005Accuracy assessment of the MODIS 16-albedo product forsnow comparison with Greenland in situ measurements RemoteSens Environ 94 46ndash60

Tedesco M 2007 Snowmelt detection over the Greenland ice sheetfrom SSMI brightness temperature daily variations GeophysRes Lett 34 L02504

van de Wal R S W Greuell W van den Broeke M Reijmer C H andOerlemans J 2005 Surface mass-balance observations andautomatic weather station data along a transect nearKangerlussuaq West Greenland Ann Glaciol 42 311ndash6

van den Broeke M R Smeet C J P P Ettema J van der Veen Cvan de Wal R S W and Oerlemans J 2008 Partitioning of energyand meltwater fluxes in the ablation zone of the west Greenlandice sheet The Cryosphere 2 179ndash89

6

Environ Res Lett 6 (2011) 014005 M Tedesco et al

primarily related to atmospheric conditions Viewed in thiscontext the unusually warm conditions over the Greenlandice sheet in 2010 and reduced snowfall can be related topersistence of a 500 hPa high ridge from late spring throughsummer Averaged for MayndashAugust 500 hPa heights wereabove normal over all of Greenland with the largest anomaliesof up to 80 m over the south-central ice sheet This anomalousridge was associated with 700 hPa temperature anomaliesover south-central Greenland of up to +3 C The ridge andassociated 700 hPa temperature anomaly was best expressed inMay and August coinciding with near-surface air temperaturerecords

Acknowledgments

This work was supported by NSF grants ANS 0909388 andARC 0901962 the NASA Cryosphere Program and the OhioState University Climate Water and Carbon Program Fieldwork along the K-transect has been supported by NWOALW

References

Abdalati W and Steffen K 1997 Snowmelt on the greenland ice sheetas derived from passive microwave satellite data J Climate10 165ndash75

Armstrong R L Knowles K W Brodzik M J and Hardman M A 1994DMSP SSMI Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media) updated 2009

Box J E Cappelen J Decker D Fettweis X Mote T Tedesco M andvan de Wal R S W 2010 Greenland (in Arctic Report Card 2010available at wwwarcticnoaagovreportcard)

Box J E and Steffen K 2001 Sublimation estimates for the Greenlandice sheet using automated weather station observationsJ Geophys Res 106 33965ndash82

Brun E David P Sudul M and Brunot G 1992 A numerical model tosimulate snowcover stratigraphy for operational Avalancheforecasting J Glaciol 38 13ndash22

Cappelen J 2010 DMI monthly climate data collection 1768ndash2009Denmark The Faroe Islands and Greenland Dansk MeterologiskInstitut Technical Report No 10-05 (available at wwwdmidkdmitr10-05pdf)

Ettema J van den Broeke M R van Meijgaard E van de Berg W JBox J E and Steffen K 2010 Climate of the Greenland ice sheetusing a high-resolution climate modelmdashpart 1 evaluationCryosph Discuss 4 561ndash602

Fettweis X 2007 Reconstruction of the 1979ndash2006 Greenland icesheet surface mass balance using the regional climate modelMAR The Cryosphere 1 21ndash40

Fettweis X 2008 Impact of ice sheet mask and resolution onestimating the surface mass balance of the Greenland ice sheetProc European Geophysical Union General Assembly (ViennaApril 2008) (available at httporbiulgacbebitstream2268367521Fettweis-2008-EGU-Poster2pdf)

Fettweis X Gallee H Lefebre L and van Ypersele J P 2005Greenland surface mass balance simulated by a regional climatemodel and comparison with satellite derived data in 1990ndash1991Clim Dyn 24 623ndash40

Fettweis X Mabille G Erpicum M Nicolay S andvan den Broeke M 2010a The 1958ndash2009 Greenland ice sheetsurface melt and the mid-tropospheric atmospheric circulationClim Dyn 36 139ndash59

Fettweis X Tedesco M van den Broeke M and Ettema J 2010bMelting trends over the Greenland ice sheet (1958ndash2009) fromspaceborne microwave data and regional climate modelsCryosph Discuss 4 2433ndash73

Hall D K Nghiem S V Schaaf C B DiGirolamo N E andNeumann G 2009 Evaluation of surface and near-surface meltcharacteristics on the Greenland ice sheet using MODIS andQuikSCAT data J Geophys Res 114 F04006

Hanna E Huybrechts P Steffen K Cappelen J Huff R Shuman CIrvine-Fynn T Wise S and Griffiths M 2008 Increased runofffrom melt from the Greenland ice sheet a response to globalwarming J Climate 21 331ndash41

Knowles K W Ein G Njoku E Armstrong R L and Brodzik M J2002 Nimbus-7 SMMR Pathfinder Daily EASE-Grid BrightnessTemperatures (Boulder CO National Snow and Ice DataCenter Digital Media)

Lefebre F Fettweis X Gallee H van Ypersele J Marbaix PGreuell W and Calanca P 2005 Evaluation of a high-resolutionregional climate simulation over Greenland Clim Dyn25 99ndash116

Lucht W Schaaf C B and Strahler A H 2000 An algorithm for theretrieval of albedo from space using semiempirical BRDFmodels IEEE Trans Geosci Remote Sens 38 977ndash98

Mote T L 2007 Greenland surface melt trends 1973ndash2007 evidenceof a large increase in 2007 Geophys Res Lett 34 L22507

Nghiem S V Steffen K Kwok R and Tsai W Y 2001 Detection ofsnowmelt regions on the Greenland ice sheet using diurnalbackscatter change J Glaciol 47 539ndash47

Stroeve J C Box J Gao F Liang S Nolin A and Schaaf C 2005Accuracy assessment of the MODIS 16-albedo product forsnow comparison with Greenland in situ measurements RemoteSens Environ 94 46ndash60

Tedesco M 2007 Snowmelt detection over the Greenland ice sheetfrom SSMI brightness temperature daily variations GeophysRes Lett 34 L02504

van de Wal R S W Greuell W van den Broeke M Reijmer C H andOerlemans J 2005 Surface mass-balance observations andautomatic weather station data along a transect nearKangerlussuaq West Greenland Ann Glaciol 42 311ndash6

van den Broeke M R Smeet C J P P Ettema J van der Veen Cvan de Wal R S W and Oerlemans J 2008 Partitioning of energyand meltwater fluxes in the ablation zone of the west Greenlandice sheet The Cryosphere 2 179ndash89

6